This invention relates to lubricating compositions which provide improved antiwear and thermal stability properties. The lubricating compositions comprise a combination of (A) at least one di or trihydrocarbyl phosphite, (B) at least one reaction product of a di or trihydrocarbyl phosphite and sulfur or a source of sulfur; at least one di or trihydrocarbyl monothiophosphate; or salt thereof, and (C) at least one salt of a hydrocarbyl phosphoric acid ester.
Lubricating compositions are used to prevent damage to machinery under operating conditions. Especially under boundary lubrication conditions, a lubricant must act to minimize harmful metal-to-metal contact. Often additives are useful at providing protection under boundary lubricating condition but sometimes these additive adversely affect other performance characteristics. For instance, a lubricant must still provide protection under high speed, shock loading condition, while not be corrosive to copper and other soft metals.
Phosphorus compounds have been used in lubricants to provide antiwear and antioxidation properties to lubricants. Phosphorus compounds generally protect metal from the effects of low speed and heavy load conditions. When the total level of phosphorus provided by the lubricant is below 0.1% by weight there have often been problems with the ability of the lubricant to provide the needed antiwear protection. In the past boron compounds, such as borated dispersants, provide thermal stability and cleanliness. It is desirable to provide additives for lubricants which provide improved antiwear properties and thermal stability.
This invention relates to a lubricating composition comprising a major amount of an oil of lubricating viscosity and (A) a di or trihydrocarbyl phosphite, (B) at least one reaction product of a di or trihydrocarbyl phosphite and sulfur or a source of sulfur; at least one di or trihydrocarbyl monothiophosphate; or salt thereof, and (C) a salt of a hydrocarbyl phosphoric acid ester. In one embodiment, the lubricant composition contains less than 0.1% phosphorus or less than about 0.75% borated dispersant. This combination of phosphorus compounds provides antiwear and thermal stability to lubricants, even at low phosphorus levels. The lubricating compositions containing the combination of the phosphorus compounds has low corrosivity to copper and low odor as well.
The term xe2x80x9chydrocarbylxe2x80x9d includes hydrocarbon as well as substantially hydrocarbon groups. Substantially hydrocarbon describes groups which contain heteroatom substituents that do not alter the predominantly hydrocarbon nature of the substituent. Examples of hydrocarbyl groups include the following:
(1) hydrocarbon substituents, i.e., aliphatic (e.g., alkyl or alkenyl) and alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, aromatic-, aliphatic-and alicyclic-substituted aromatic substituents and the like as well as cyclic substituents wherein the ring is completed through another portion of the molecule (that is, for example, any two indicated substituents may together form an alicyclic radical);
(2) substituted hydrocarbon substituents, i.e., those substituents containing non-hydrocarbon groups which, in the context of this invention, do not alter the predominantly hydrocarbon nature of the substituent; those skilled in the art will be aware of such groups (e.g., halo (especially chloro and fluoro), hydroxy, mercapto, nitro, nitroso, sulfoxy, etc.);
(3) heteroatom substituents, i.e., substituents which will, while having a predominantly hydrocarbon character within the context of this invention, contain an atom other than carbon present in a ring or chain otherwise composed of carbon atoms (e.g., alkoxy or alkylthio). Suitable heteroatoms will be apparent to those of ordinary skill in the art and include, for example, sulfur, oxygen, nitrogen and such substituents as, e.g. pyridyl, furyl, thienyl, imidazolyl, etc.
In general, no more than about 2, preferably no more than one heteroatom substituent will be present for every ten carbon atoms in the hydrocarbyl group. Typically, there will be no such heteroatom substituents in the hydrocarbyl group. Therefore, the hydrocarbyl group is hydrocarbon.
Generally the total phosphorus for the lubricant is determined by the amount of all phosphorus components added to the lubricant. The amount of phosphorus in the lubricating composition is sufficient to provide a pass result in the ASTM L-37 test. The total phosphorus is usually less than about 0.1%, or less than 0.09%, or less than about 0.08% by weight. In one embodiment, the phosphorus compounds of the present invention are present at phosphorus contents of less than about 0.07, or less than about 0.06% by weight phosphorus.
As described above the lubricating composition comprise a combination of (A) at least one di or trihydrocarbyl phosphite, (B) at least one reaction product of a phosphite and sulfur or a source of sulfur; at least one di or trihydrocarbyl monothiophosphate; or salt thereof, and (C) at least one salt of a hydrocarbyl phosphoric acid ester. Each component of the combination may be independently present in an amount to provide from about 0.01% to about 0.06%, or from about 0.012% to about 0.05%, or from about 0.018% to about 0.04% by weight phosphorus to the lubricant. Here, as well as elsewhere in the specification and claims, the range and ratio limits may be combined. In one embodiment, each component is present in substantially equal phosphorus proportions. In another embodiment, each component is independently present in an amount from about 0.05% to about 2%, or from about 0.08% to about 1%, or from about 0.1xc2x0% to about 0.6% by weight.
As described herein and in the appended claims, it is understood that any element listed within a genus or list may be excluded from the claims.
(A) Phosphites
As described above the lubricating compositions, concentrates, and greases contain at least one phosphite. The phosphite may be a di- or trihydrocarbyl phosphite. Preferably each hydrocarbyl group contains from 1 to about 24 carbon atoms, or from 1 to about 18 carbon atoms, or from about 2 to about 8 carbon atoms. Each hydrocarbyl group may be independently alkyl, alkenyl, or aryl, preferably alkyl or alkenyl. When the hydrocarbyl group is an aryl group, then it contains at least about 6 carbon atoms; preferably about 6 to about 18 carbon atoms. Examples of the alkyl or alkenyl groups include propyl, butyl, hexyl, heptyl, octyl, oleyl, linoleyl, stearyl, etc. Examples of aryl groups include phenyl, naphthyl, heptylphenol, etc. Preferably each hydrocarbyl group is independently propyl, butyl, pentyl, hexyl, heptyl, oleyl or phenyl, more preferably butyl, oleyl or phenyl and more preferably butyl or oleyl. In one embodiment, the phosphite is an alkyl or alkyenyl, preferably an alkyl phosphite. In another embodiment, the lubricating compositions are free of phosphites with hydrocarbyl groups that are aryl groups. One method of preparing phosphites includes reacting a lower (C1-8) Phosphites and their preparation are known and many phosphites are available commercially. Particularly useful phosphites are dibutyl hydrogen phosphite, dioleyl hydrogen phosphite, di(C14-18) hydrogen phosphite, and triphenyl phosphite.
In another embodiment, the phosphite is premixed with a overbased metal salt of an organic acid, wherein the equivalents of overbased metal salt, based on total base number to the equivalents of phosphite (A) based on phosphorus atoms is at least one. The inventors have discovered that by pre-mixing the phosphite in the overbased metal salt of an acidic organic compound, the hydrostability of the phosphite is improved. Overbased metal compositions are characterized by having a metal content in excess of that which would be present according to the stoichiometry of the metal and the acidic organic compound. The amount of excess metal is commonly expressed in metal ratio. The term xe2x80x9cmetal ratioxe2x80x9d is the ratio of the total equivalents of the metal to the equivalents of the acidic organic compound. A salt having a metal ratio of 4.5 will have 3.5 equivalents of excess metal. The overbased salts generally have a metal ratio from about 1.5 up to about 40, or from about 2 up to about 30, or from about 3 up to about 25.
The overbased materials are prepared by reacting an acidic material, typically carbon dioxide, with a mixture comprising an acidic organic compound, a reaction medium comprising at least one inert, organic solvent for the acidic organic compound, a stoichiometric excess of a basic metal compound, and a promoter. Generally, the basic metal compounds are oxides, hydroxides, chlorides, carbonates, and phosphorus acids (phosphonic or phosphoric acid) salts, and sulfur acid (sulfuric or sulfonic) salts. The metals of the basic metal compounds are generally alkali, alkaline earth, and transition metals. Examples of the metals of the basic metal compound include sodium, potassium, lithium, magnesium, calcium, barium, titanium, manganese, cobalt, nickel, copper, and zinc, preferably sodium, potassium, calcium, and magnesium, more preferably calcium and magnesium.
The acidic organic compounds useful in making the overbased compositions of the present invention include carboxylic acylating agents, such as polyalkenyl succinic anhydrides, sulfonic acids, phosphorus-containing acids, phenols, or mixtures of two or more thereof. Preferably, the acidic organic compounds are carboxylic acylating agents, sulfonic acids, or phenates. In one embodiment the overbased material is a calcium or magnesium, preferably magnesium, overbased sulfonate or salicylate.
The methods for preparing the overbased materials, as well as overbased materials, are known in the prior art and are disclosed, for example, in the following U.S. Pat. Nos. 2,616,904; 2,616,905; 2,616,906; 3,242,080; 3,250,710; 3,256,186; 3,274,135; 3,492,231; and 4,230,586. These patents disclose processes, materials, which can be overbased, suitable metal bases, promoters, and acidic materials, as well as a variety of specific overbased products useful in producing the overbased systems of this invention and are, accordingly, incorporated herein by reference for these disclosures.
(B) Thiophosphate or Reaction Products of Phosphite and Sulfur or a Source of Sulfur
As described above the lubricating compositions, concentrates, and greases contain at least one reaction product of a phosphite and sulfur or a source of sulfur; at least one thiophosphate; or a salt thereof. Component (B) may be a dihydrocarbyl thiophosphate, a trihydrocarbyl thiophosphate, or mixture thereof. In one embodiment, the phosphites used to make component (B) may be any of the above described phosphites. Preferably this phosphite is a trihydrocarbyl phosphite, more preferably a triaryl phosphite. The hydrocarbyl group typically contain from about 4 to about 24, or from about 5 to about 18, or from about 6 to about 12 carbon atoms. Examples of useful hydrocarbyl groups include benzyl, methylbenzyl, dimethylbenzyl, methoxyphenyl, etc. A particularly useful phosphite for preparing component (B) is triphenylphosphite.
As discussed above the phosphite is reacted with sulfur or a source of sulfur. The sulfur source may be any of a variety of materials which are capable of supplying sulfur to the reaction. Examples of useful sulfur sources include sulfur halides, combinations of sulfur or sulfur oxides with hydrogen sulfide, and various sulfur containing organic compounds. The sulfur halides include sulfur monochloride, sulfur dichloride, etc. The sulfur sources may also be sulfur containing organic compounds, such as aromatic and alkyl sulfides, dialkenyl sulfides, sulfurized olefins, sulfurized oils, sulfurized fatty acid esters, sulfurized aliphatic esters of olefinic mono- or dicarboxylic acids, diester sulfides, sulfurized Diels-Alder adducts and sulfurized terpenes. U.S. Pat. No. 4,755,311 discloses various sulfur sources capable of supplying sulfur to reaction. This patent is incorporated by reference for its disclosure of sulfur sources. The sulfur source may also be those sulfur compounds disclosed below.
In one embodiment, the component (B) is at least one compound of the structure:
(RX)3P=X
where each X is independently sulfur or oxygen, provided that at least one X is sulfur, and wherein each R is independently a hydrocarbyl group. The hydrocarbyl groups are described above. In one embodiment, the hydrocarbyl groups for the above formula are those described for the phosphites above.
Triphenylthiophosphate is sold by Ciba-Geigy under the trade name Irgalube TPPT(trademark). Other suitable monothiophosphates include tricresylthiophosphate, tri-p-dodecylphenylthiophosphate, trioctylthiophosphate, tri-p-t-butylphenylthiophosphate, tri-xcex2-naphthylthiophosphate, trilaurylthiophosphate, tri-p-heptylphenylthiophosphate, thiophosphates based on sulfur-coupled alkylphenols.
The following example relates to preparation of thiophosphates.